Patent Application
20200110349
This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2018-188491 filed on Oct. 3, 2018, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a developing device incorporated in an image forming apparatus such as copies, printers, and facsimile machines. In particular, the present disclosure relates to a method for preventing developer from clogging in a gap between a developing roller and a regulating blade.
In one conventionally common process as an image developing method in image forming apparatuses using an electro-photographic process, powder developer is mainly used, an electrostatic latent image formed on an image carrying member such as a photosensitive drum is made visible with the developer, and the visible image (toner image) is transferred to a recording medium and is then fixed.
Developer is roughly divided into two-component developer containing toner and magnetic carrier and one-component developer containing non-magnetic or magnetic toner alone. As a developing method using magnetic one-component developer, a so-called jumping one-component developing method is known, according to which a fixed magnet member having a plurality of magnetic poles is arranged inside a developing roller, toner in a developer container is carried on the developing roller by use of a magnetic carrying force, a thin layer of toner is formed through layer thickness regulation by use of a regulating blade, and toner is made to fly to a photosensitive drum at a developing position.
In recent years, low-melting-point toner is increasingly used for energy saving and acceleration of printing. When continuous printing is performed in a high-temperature environment by use of low-melting-point toner, toner stagnating at a place where the developing roller and the regulating blade face each other (regulating portion) softens due to heat or mechanical stress and causes blocking, resulting in clogging in a gap in the regulating portion. This inconveniently results in unevenness in a toner layer on the developing roller, producing vertical streaks such as white streaks and gray streaks on the output image.
To avoid that, for example, toner and a developing system excellent in low-temperature fixability, high-temperature-resistant offset property, and blocking resistance have been developed. According to one known method, the regulating height of the regulating blade in opposite end parts thereof facing near opposite end parts of the developing roller is set higher than in other parts, and thereby compression (high density) of developer in the opposite end parts of the developing roller is reduced, in order to thereby prevent developer agglomeration.
According to another known method, the angle of arrangement of a magnetic field generating means having a plurality of magnetic poles arranged inside the developer carrying member is changed according to the use environment of and the manner of use of the image forming apparatus, in order to thereby improve degraded image quality resulting from lowered image density and fogging due to a white part.
According to one aspect of the present disclosure, a developing device includes a housing, a developer carrying member, a regulating blade, and a magnetic member. The developing device develops an electrostatic latent image formed on an image carrying member. The housing stores magnetic developer. The developer carrying member is rotatably supported on the housing and carries the developer on the circumferential face. The regulating blade is formed of a magnetic material, is arranged at a predetermined interval from the developer carrying member, and forms a regulating portion that regulates the thickness of the developer carried on the developer carrying member. The magnetic member is arranged inside the developer carrying member and has a plurality of magnetic poles including a regulating pole arranged at a position where the developer carrying member and the regulating blade are close together. The regulating pole is movable to a first position that faces the regulating portion and to a second position rotated to the upstream side through a predetermined angle from the first position with respect to the rotation direction of the developer carrying member during image formation. The developing device is operable in a developer removing mode in which, when no image is formed, the regulating pole is moved from the first position to the second position and is then returned to the first position to remove the developer stagnating in the regulating portion.
Further features and advantages of the present disclosure will become apparent from the description of embodiments given below.
Hereinafter, with reference to the accompanying drawings, embodiments of the present disclosure will be described.
In the image forming portion 9, along the rotation direction (the clockwise direction) of the photosensitive drum 1, there are arranged a charging device 2, an exposure unit 3, a developing device 4, a transfer roller 6, a cleaning device 7, and a static eliminator (unillustrated). The photosensitive drum 1 is, for example, an aluminum drum laid with a photosensitive layer, and its surface is electrostatically charged uniformly by the charging device 2. Then, on the surface irradiated with a laser beam from the exposure unit 3, which will be described later, an electrostatic latent image with attenuated electrostatic charge is formed. There is no particular restriction on the photosensitive layer, which preferably is, for example, a layer of amorphous silicon (a-Si), which excels in durability, or the like.
The charging device 2 electrostatically charges the surface of the photosensitive drum 1 uniformly. As the charging device 2, for example, a corona discharge device is used which causes electric discharge by applying a high voltage to a thin wire or the like acting as an electrode. Usable instead of the corona discharge device is a contact-type charging device which applies a voltage while keeping the surface of the photosensitive drum 1 in contact with a charging member as exemplified by a charging roller. The exposure unit 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on image data to form an electrostatic latent image on the surface of the photosensitive drum 1.
The developing device 4 forms a toner image by attaching toner to the electrostatic latent image on the photosensitive drum 1. In this embodiment, magnetic one-component developer (hereinafter, referred to as toner) comprising magnetic toner is stored in the developing device 4. The developing device 4 will be described in detail later. The cleaning device 7 includes a cleaning roller, a cleaning blade, or the like that makes line contact with the photosensitive drum 1 in its longitudinal direction (the direction perpendicular to the plane of
Toward the photosensitive drum 1 having the toner image formed on it as described above, a sheet is conveyed from a sheet storage portion 10 via a sheet conveying passage 11 and a registration roller pair 13 to, with a predetermined timing, the image forming portion 9. The transfer roller 6 moves (transfers), without disturbing, the toner image formed on the surface of the photosensitive drum 1 to a sheet conveyed through the sheet conveying passage 11. Thereafter, in preparation for subsequent formation of new electrostatic latent images, toner left unused on the surface of the photosensitive drum 1 is removed by the cleaning device 7, and electric charge remaining is removed by the static eliminator.
The sheet having the toner image transferred to it is separated from the photosensitive drum 1, and is conveyed to a fixing device 8, where the toner image is heated and pressed so as to be thereby fixed to a sheet. The sheet having passed through the fixing device 8 passed through a discharge roller pair 14 and is discharged onto a sheet discharge portion 15.
The first and second stirring screws 23 and 24 are each composed of a helical blade arranged around a support shaft (rotary shaft) and are rotatably supported on the housing 20 so as to be parallel to each other. As shown in
The developing roller 25 rotates as the photosensitive drum 1 (see
A regulating blade 29 is formed so as to be, in its longitudinal direction (in
The bottom face of the second storage chamber 22 facing the second stirring screw 24 is provided with a toner amount detection sensor (unillustrated) that detects the amount of toner stored in the housing 20. According to the result of detection by the toner amount detection sensor, the toner stored in the toner container 5 (see
DS rollers 31a and 31b are rotatably fitted outside the rotary shaft of the developing roller 25. The DS rollers 31a and 31b make contact with opposite end parts, in the axial direction, of the circumferential face of the photosensitive drum 1, and thereby precisely regulate the distance between the developing roller 25 and the photosensitive drum 1. The DS rollers 31a and 31b each incorporate a bearing and rotate by following the photosensitive drum 1 as it rotates; this helps prevent its surface from wearing. At opposite end parts of the developing roller 25 in the axial direction, magnetic sealing members 33a and 33b are arranged for preventing toner from leaking through a gap between the housing 20 and the developing roller 25.
As shown in
To one end of the shaft 27e, the driving input gear 37 is fixed, and to the driving input gear 37, a magnet drive motor 43 (see
Back in
By the magnetic field, a magnetic brush composed of chains of toner particles is formed between the regulating blade 29 and the developing roller 25, and when the magnetic brush passes through the regulating portion 30, its layer is regulated to a desired height. On the other hand, the toner left unused in forming the magnetic brush stagnates along a side face of the regulating blade 29 on its upstream side (right side). Then, when the developing roller 25 rotates in the counter-clockwise direction and the magnetic brush moves to a region (developing region) facing the photosensitive drum 1, a magnetic field is applied by the N1 pole (main pole) 27b to the magnetic brush; thus, the magnetic brush makes contact with the surface of the photosensitive drum 1 and develops an electrostatic latent image.
When the developing roller 25 rotates further in the counter-clockwise direction, a magnetic field is applied by the S1 pole (conveying pole) 27a now in the direction along the circumferential face of the developing roller 25; thus, the toner left unused in forming the magnetic brush is, together with the magnetic brush, collected on the developing roller 25. Then, the magnetic brush is separated from the developing roller 25 in a hollow part between the S1 pole 27a and the N2 pole 27d, and falls into the housing 20. Then, after being stirred and conveyed by the second stirring screw 24, a magnetic brush is again formed on the developing roller 25 by the magnetic field from the N2 pole (draw-up pole) 27d.
In the housing 20 surrounding the opposite end parts of the developing roller 25, the magnetic sealing members 33a and 33b are arranged, respectively. In
A developing drive part 40 includes a developing drive motor 41, a developing clutch 42, and a magnet drive motor 43. The developing drive motor 41 drives the first and second stirring screws 23 and 24 and the developing roller 25 to rotate. The developing clutch 42 turns on and off the rotation driving force that is fed from the developing drive motor 41 to the first and second stirring screws 23 and 24 and the developing roller 25. By rotating the shaft 27e, the magnet drive motor 43 rotates the fixed magnet member 27 fixed on the shaft 27e through a predetermined angle.
A voltage control circuit 51 is connected to a charging voltage power supply 52, a developing voltage power supply 53, and a transfer voltage power supply 54, and operates those power supplies according to output signals from a control portion 90. Those power supplies operate according to control signals from the voltage control circuit 51 such that predetermined voltages are applied from the charging voltage power supply 52 to a wire in the charging devices 2, from the developing voltage power supply 53 to the developing roller 25 in the developing device 4, and from the transfer voltage power supply 54 to the transfer roller 6.
An image input portion 60 is a receiving portion which receives image data transmitted from a PC or the like to the image forming apparatus 100. The image signal fed from the image input portion 60 is converted into a digital signal, and is then fed out to a temporary memory 94.
An interior temperature and humidity sensor 61 serves to sense the temperature and humidity inside the image forming apparatus 100, in particular, the temperature and humidity of and around the developing device 4, and is arranged near the image forming portion 9.
An operation portion 70 includes a liquid crystal display portion 71 and an LED 72 which indicates various statuses. The operation portion 70 indicates the status of the image forming apparatus 100, and displays the progress of image formation and the number of copies printed. Various settings for the image forming apparatus 100 are made via the printer driver on a PC.
The control portion 90 includes at least a CPU (central processing unit) 91 as a central processor device, a ROM (read-only memory) 92 which is a memory for reading only, a RAM (random-access memory) 93 which is a memory for both reading and writing, a temporary memory 94 which temporarily stores image data and the like, a counter 95, and a plurality of (here, two) I/Fs (interfaces) 96 which transmit control signals to different blocks in the image forming apparatus 100 and which receive input signals from the operation portion 70.
The ROM 92 stores data and the like which are not changed during the use of the image forming apparatus 100, such as a program for control of the image forming apparatus 100 and values necessary for control. The RAM 93 stores necessary data generated in the process of controlling the image forming apparatus 100, data temporarily needed to control the image forming apparatus 100, and the like. The RAM 93 (or the ROM 92) also stores a table that defines a relationship of the temperature and humidity detected by the interior temperature and humidity sensor 61 and the cumulative number of printed sheets counted by the counter 95 with respect to the rotation angle of the fixed magnet member 27, which will be described later.
The temporary memory 94 temporarily stores an image signal which is fed from the image input portion 60 receiving image data transmitted from a PC or the like and which is then converted into a digital signal. The counter 95 counts the number of printed sheets on a cumulative basis.
The control portion 90 transmits control signals from the CPU 91 via the I/Fs 96 to different blocks and devices in the image forming apparatus 100. From the different blocks and devices, signals showing their status and input signals are transmitted via the I/Fs 96 to the CPU 91. The different blocks and devices controlled by the control portion 90 include, for example, the fixing device 8, the image forming portion 9, the developing drive part 40, the voltage control circuit 51, the image input portion 60, and the operation portion 70.
As described earlier, when continuous printing is performed in a high-temperature environment by use of low-melting-point toner as magnetic one-component developer, toner stagnating in the regulating portion 30 in the developing device 4 softens and causes blocking (agglomeration), resulting in clogging. As a remedy, in this embodiment, the developing device 4 can operate in a developer removing mode in which, when no image is formed, the fixed magnet member 27 inside the developing roller 25 is rotated through a predetermined angle to remove the toner (developer) stagnating in the regulating portion 30.
When a print instruction is fed in from a host device such as a PC and printing is started (step S1), the control portion 90 (see
If the cumulative number of printed sheets has reached the prescribed number of sheets (step S3, Yes), in response to a control signal from the control portion 90, sheets stop being fed from the sheet storage portion 10 (step S4). Also, the developing voltage stops being applied from the developing voltage power supply 53 (see
Then, a control signal is fed from the control portion 90 to the magnet drive motor 43 (see
Thus, as shown in
Next, the fixed magnet member 27 is rotated in the forward direction (in
Through the control in
Specifically, even when low-melting-point toner with a glass transition point (Tg) of 55° C. or less is used in a developing system in which the developing roller 25 has a liner velocity (process speed) of 500 mm/sec or more and in addition continuous printing is repeated in a high-temperature environment, toner does not stagnate in the regulating portion 30, and blocking with toner resulting from heat or mechanical stress is suppressed. It is thus possible to effectively prevent toner clogging in the regulating portion 30 and the resulting image defects such as white streaks or gray vertical streaks.
If the rotation angle of the S2 pole 27c from the first position to the second position is too small, it is impossible to obtain a sufficient effect of making the toner stagnating in the regulating portion 30 flow. On the other hand, if the rotation angle of the S2 pole 27c from the first position to the second position is too large, the S1 pole 27a and the N1 pole 27b of the fixed magnet member 27 also rotate as much, and thus toner carried on the part of the developing roller 25 exposed outside the housing 20 is scattered by movement of the S1 pole 27a and the N1 pole 27b. The scattered toner attaches to the outer side face (in
Although, in the example of control in
Furthermore, it is possible to change, according to the result of detection by the interior temperature and humidity sensor 61, the rotation angle of the S2 pole 27c from the first position to the second position during execution of the developer removing mode or the number of times of movement of the S2 pole 27c during execution of the same mode or the frequency of execution of the developer removing mode. That is, the higher the interior temperature, the lower the flowability of toner, and thus the more likely blocking and agglomeration are to occur; thus, by increasing the rotation angle of the S2 pole 27c from the first position to the second position, increasing the number of times of movement, and increasing the frequency of execution (shortening intervals) of the developer removing mode, it is possible to suppress toner agglomeration and thus to prevent image defects effectively.
Instead of the interior temperature and humidity sensor 61, an exterior temperature sensor that senses the temperature outside (exterior temperature of) the image forming apparatus 100 can be provided, and according to the exterior temperature detected by the exterior temperature sensor, the rotation angle of the S2 pole 27c from the first position to the second position during execution of the developer removing mode or the number of times of movement during execution of the same mode or the frequency of execution of the developer removing mode can be changed.
In this embodiment, when the developing device 4 operates in the developer removing mode, the developing roller 25 is rotated in the backward direction through a predetermined angle (step S6), and the S2 pole 27c is moved from the first position to the second position (step S7) and is then returned to the first position (step S8). Otherwise, the operation here is similar to that in the first embodiment shown in
In this embodiment, in addition to variation of the magnetic force pattern around the regulating portion 30 resulting from movement of the S2 pole 27c from the first position to the second position, a physical force resulting from rotation of the developing roller 25 in the backward direction acts on the toner stagnating around the regulating portion 30. Thus, compared with the first embodiment, it is easier to make the toner stagnating in the regulating portion 30 flow, and it is thus possible to more effectively prevent toner clogging in the regulating portion 30 and image defects such as white streaks or gray vertical streaks. That is, it is possible to reduce the rotation angle of the S2 pole 27c, to reduce the number of times of movement, and to reduce the frequency of execution of the developer removing mode; this makes it possible to improve the efficiency of image formation.
As in the first embodiment, it is possible to change, according to the result of detection by the interior temperature and humidity sensor 61, the rotation angle of the S2 pole 27c from the first position to the second position during execution of the developer removing mode or the number of times of movement during execution of the same mode or the frequency of execution of the developer removing mode.
The present disclosure may be implemented in any other manner than in the embodiments described above, and allows for many modification without departure from the spirit of the present disclosure. Although, for example, in the above-described embodiments, the fixed magnet member 27 has four poles including two N poles and two S poles, the present disclosure is applicable equally to a fixed magnet member 27 having five poles or three poles.
Although, the embodiments described above deal with the developing device 4 using magnetic one-component developer, the present disclosure is applicable equally to a developing device using two-component developer containing magnetic carrier and non-magnetic toner. When two-component developer is used, the magnetic force acting between the developing roller 25 or the regulating blade 29 and the magnetic carrier contained in the developer varies, and so does the magnetic force acting among carrier particles vary; this makes the two-component developer stagnating in the regulating portion 30 flow; it is thus possible to prevent toner agglomeration and clogging in the regulating portion 30 resulting from blocking with two-component developer. Below, by way of practical examples, the effects of the present disclosure will be described more specifically.
The relationship between the melting point of toner (Tg), the frequency of execution of the developer removing mode, and the movement angle of the regulating pole (S2 pole 27c) with image defects was studied. In the test, a test machine (an altered version of the model FS-4300 manufactured by Kyocera Document Solutions Inc.) was used, and the developing roller 25 was rotates at a liner velocity of 574 mm/sec. Whether and how image defects occurred was inspected visually while the developing device 4 operated in the developer removing mode in which, during continuous printing of 3000 sheets (500 sheets×6 times) in a 33° C. environment, printing was stopped and the S2 pole 27c was moved from the first position to the second position and was then returned to the first position for every 100 sheets (30 times), 500 sheets (6 times), and 1000 sheets (3 times).
The movement angle of the regulating pole from the first position to the second position was set at six different levels, namely 0° (no movement), 5°, 15°, 40°, 75°, and 90°. Also, three different types of toner of which the toner resin had a Tg of 45° C., 55° C., and 60° C., respectively, were used.
The criteria for evaluation were as follows: a condition where there was no defect in a toner layer on the developing roller 25 was evaluated as good, a condition where there was unevenness (toner streaks or soil) in a toner layer on the developing roller 25 but there was no image defect was evaluated as fair, and a condition where there was a defect on the output image was evaluated as poor. Table 1 shows the results.
The test results were as follows. In a case where toner of which the toner resin had a Tg of 45° C. was used, when the movement angle of the regulating pole was set at 0° (no movement) and 5° in the developer removing mode, white streaks appeared in the image. When the movement angle was set at 15°, toner streaks appeared on the developing roller 25 but no white streaks appeared on the image. Then, when the movement angle was set at 45° and the frequency of execution of the developer removing mode was set for every 100 sheets, or when the movement angle was set at 75°, no toner streaks appeared on the developing roller 25 either any longer. These results indicate that, by increasing the movement angle of the regulating pole in the developer removing mode and the frequency of execution of the developer removing mode, it is possible to prevent the appearance of white streaks in the image and toner streaks on the developing roller 25.
However, when the movement angle was set at 90°, toner attracted by the magnetic force acting in the backward direction with respect to the rotation direction of the developing roller 25 during printing soiled the surface of the regulating blade 29 among others. Although no image defect was observed during continuous printing of 3000 sheets, it is feared that, as printing continues, soil may accumulate and this may lead to image defects. Thus, the movement angle of the regulating pole is considered to need to be within a predetermined angle range (15° to 75°) and is preferably within a range of 40° to 75°.
Also indicated is the following. With the toner of which the toner resin had a Tg of 55° C. or 60° C., the appearance of white streaks on the image and of toner streaks tended to reduce; compared with the toner of which the toner resin had a Tg of 55° C. or 60° C., the toner of which the toner resin had a Tg of 45° C. provided a greater effect of changing the angle of the regulating pole. Thus, it is considered that toner with lower thermal characteristics (toner of which the toner resin has a Tg of 55° C. or less) suitable for energy saving provides a greater effect of preventing blocking with toner through execution of the developer removing mode in which the regulating pole is moved.
In the test, except than that the developing roller 25 was rotated through 45° in the backward direction during execution of the developer removing mode, the methods and the criteria for evaluation here were similar to those in Practical Example 1. Table 2 shows the results.
The test results were as follows. In a case where the developing roller 25 was rotated in the backward direction during execution of the developer removing mode, with toner of which the toner resin had a Tg of 45° C., when the movement angle of the regulating pole was set at 5° and the frequency of execution of the developer removing mode was set for every 500 sheets or less, no white streaks appeared on the image any longer. Also, when the movement angle was set at 15° and the frequency of execution of the developer removing mode was set for every 500 sheets or less, no toner streaks appeared on the developing roller 25.
That is, by rotating the developing roller 25 in the backward direction during execution of the developer removing mode, compared with a case where the developing roller 25 was not rotated in the backward direction, a satisfactory effect of preventing white streaks in the image and toner streaks on the developing roller 25 was obtained. These results indicate that, by both rotating the developing roller 25 in the backward direction and changing the angle of the regulating pole in the developer removing mode, it is possible to more effectively prevent blocking with toner.
The present disclosure is applicable to a developing device that uses magnetic developer. Based on the present disclosure, it is possible to provide a developing device that can prevent developer clogging in a regulating portion even when continuous printing is performed in a high-temperature environment, and to provide an image forming apparatus incorporating such a developing device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-188491 | Oct 2018 | JP | national |
